1. Field of the Invention
The present invention relates to an electronic endoscope having exposed metal at a distal end.
2. Description of the Related Art
As is well known, endoscopes are widely used for observation, treatment, and the like inside a body (inside a body cavity) of a living body or for inspection, repair, and the like in industrial plant equipment. Among endoscopes, electronic endoscopes including an image pickup apparatus with a CCD and the like placed in the image pickup apparatus have recently become mainstream. In such a conventional electronic endoscope, a holding frame made of metal which holds an optical member on a side closer to a distal end than a CCD is disposed at a distal end portion.
In the conventional electronic endoscope, fogging due to condensation may occur in an objective optical system, resulting from a temperature difference between outside air temperature and ambient temperature of an object to be examined, ambient humidity in the object to be examined, and the like. For the reason, various techniques for preventing, e.g., fogging of and condensation on an outer surface of a transparent cover member of an objective optical system have been proposed for endoscopes. For example, Japanese Patent Application Laid-Open Publication No. 2009-261830 discloses a defogging technique in an objective optical system in which an anti-fogging device which heats a thin film formed on a cover glass arranged at a distal end portion of an electronic endoscope is provided at a holding frame for the cover glass.